Fiber optic cable furcation unit

ABSTRACT

A low cost rugged sealed fiber optic cable furcation unit is provided. Theurcation unit has an outer heat shrink tube which encloses a protective tube. Within the protective tube, a spacer/fiber guide is located along with a sealant material. When installed and sealed, the sealed furcation unit includes fiber ends and cables. The furcation unit allows loose tube fiber optic cables or tube ducts within Air Blown Fiber (AEF) cables to be furcated into multiple single fiber cables. The furcation unit is compatible with both 250 micrometer and 500 micrometer coated optical fibers. The furcation unit is also compatible with common single fiber optical connectors and splices.

This application is a continuation of copending application Ser. No.08/944,105 filed on Sep. 30, 1997 now is U.S. Pat. No. 5,903,693.

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of officialduties by an employee of the Department of the Navy and may bemanufactured, used, licensed by or for the Government for anygovernmental purpose without payment of any royalties thereon.

FIELD OF THE INVENTION

The present invention relates generally to optical fiber connectors andmore specifically to furcation units for optical fiber cables.

BACKGROUND OF THE INVENTION

In recent years, electro-optical equipment has begun to replaceelectronic equipment for certain applications, such as telecommunicationand data communication networks. This trend should continue because theelectro-optical equipment has inherent advantages over purely electronicequipment. These advantages include a broader bandwidth for signaltransmission, greater storage capability for data, and inherent immunityto electromagnetic interference. Given these advantages ofelectro-optical equipment, fiber optic cables have become increasinglyimportant because they transmit information and signals between thevarious pieces of electro-optical equipment.

The appearance of these cables resemble electrical cables, but fiberoptic cables are smaller in size and lighter in weight. Fiber opticcables comprise optical fibers and other cable elements which areprotected from the external environment by an external jacketing. Thesecables may be of a traditional design with the fibers surrounded bystrength members and protective elements in the cable core or of a morenon-traditional, loosely-bundled type with the fibers contained looselywithin tubes or ducts in a cable core.

Whether traditional or loosely-bundled, all types of optical fibercables may contain groups of optical fibers with no individualprotective jacketing or strength members. These fibers are typically 250micrometers or 500 micrometers in diameter. At the ends of the fiberoptic cables, the small unprotected fibers must be removed from theouter protective cable structure and inserted into fiber opticconnection devices (connectors or splices). Due to the small size of thefibers and the lack of protective coverings over the individual fibers,connectorization and splicing is difficult. Special protective equipmentmust be used to organize the loose fibers and to protect the completedconnections. In order to make the installation of fiber cables reliableand efficient, a furcation unit is needed which allows individualoptical fibers to be easily handled, connectorized, and spliced.Further. in order to prevent degradation of the prepared fibers, thefurcation unit must protect the fiber ends from moisture, dust, andother contaminants.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide adevice to mechanically protect optical fibers exposed at a fiber opticcable termination point.

Another object of the invention is to provide a device to seal the endof the fiber optic cable against moisture, dirt and insects.

Another object of the invention is to provide connector installer with acable end that is compatible with typical single fiber opticalconnectors and splices.

A further object of the present invention is to provide a means fororganizing single fiber stands within a multi-fiber optical cable.

A still further object of the present invention is to provide a simpleto use furcation unit allowing for fast, efficient installation by fieldtechnicians.

In accordance with the foregoing and additional objects, a sealed fiberoptic cable furcation unit is provided. The furcation unit comprises anouter heat shrink tubing containing a concentrically-located protectivetube which, in turn, contains a spacer/fiber guide and sealant material.The furcation unit allows the sealed connection of a single cablecontaining multiple fibers with multiple cables containing individualfibers. The furcation unit seals the end of the fiber optic cable andguides the fibers into protective loose tube single fiber cablessuitable for handling and termination. When sealed, the furcation unitincludes the prepared ends of the multiple cables and the single cablescontaining multiple fibers. The single fiber cables are securelyattached within the furcation unit using adhesive to prevent accidentalremoval of any members of the single fiber cable from the furcation unitduring connectorization or splicing operations.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects and other advantages of the present invention willbe more fully understood from the following detailed description andreference to the appended drawings wherein:

FIG. 1 is a cross-sectional view of the fiber optic cable furcationunit; and

FIG. 2 is an expanded cross-sectional view of the portion of the fiberoptic cable furcation unit containing the ends of the loose tube singlefiber optical cables.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, fiber optical cable furcation-unit 10 forfurcating fiber optic cables is shown. The furcation unit 10 comprisesan adhesive coated heat shrink tubing 11, enclosing a protective tube 13and a sealant material 15. The furcation unit 10 further comprises aplurality of loose tube single fiber optical cables 21 and aspacer/fiber guide 31. The furcation unit 10 fits onto the end of afiber optic cable 41 allowing the optical fibers 42 to pass through thespacer/fiber guide 31 and protective tube 13 into the loose tube singlefiber optical cables 21. The adhesive coated heat shrink tubing 11securely holds the furcation unit 10 onto the optical fiber cable 41 andfirmly holds the protective tube 13 and the multiple loose tube singlefiber optical cables 21 in position. In the preferred embodiment, theheat shrink tubing is a polyolefin tube and the protective tube is apolyethylene plastic tube. The furcation unit 10, when constructed inthis manner, is extremely rugged and can withstand bending, dropping,tensile loads and other rigors. The sealant material 15 fills any voidsin the end of the fiber optic cable 41, and further fills any voidsbetween the fiber optic cable 41 and the protective tube 13. A varietyof sealant materials may be used including silicone sealants or othersimilar material. The sealant material 15 also fills a short lengthwithin the interior of the protective tube 13, thereby completing thesealing of the furcation unit 10 to the fiber optic cable 41. Thespacer/fiber guide 31 loosely fits within the protective tube 13 and maybe held in place by the sealant material 15. Depending on the type offiber optic cable, the spacer/fiber guide 31 may not be required.

Referring now to FIG. 2, the loose tube single fiber cables eachcomprise an inner tube 23, strength members 25, and an outer protectivejacketing 27. The loose tubes can be fabricated using nylon tubes andthe strength members may be fabricated using an arimid fiber material.In the preferred embodiment, Kevlar™ fiber is used for the strengthmembers. The inner tube 23 is dimensioned so that the optical fibers 42can easily be passed through a length of the tube and so that the innertube 23 can be inserted into the rear of common fiber optic connectorsand splices. The strength members 25 are used within the loose tubesingle fiber cables 21 to allow proper termination of the optical fiber42 into fiber optic connectors and splices which are designed to attachto a single fiber cable strength member. The strength members 25protrude from the interior end of the loose tube single fiber cables 21and are folded back along the exterior of the loose tube single fibercables and are captured in the adhesive matrix 43, (in this case atwo-part epoxy adhesive). Captured in this manner, the loose tube singlefiber cable 21 cannot be accidentally pulled out of the furcation unit10 during the optical fiber 42 termination process. The inner tubes 23also protrude from the interior end of the loose tube single fibercables 21. Thus, the optical fiber 42 is never in contact with anyadhesive material used in the adhesive matrix 43. In addition, theadhesive matrix 43 seals the end of the furcation unit 10 where theloose tube single fiber optical cables 21 are contained, keepingmoisture, dirt, and insects out of the interior of the furcation unit10.

In some cases the inner tubes 23 may be extended through the sealantmaterial 15 into the fiber optic cable 41 (as shown in FIG. 1). Thisapproach is advantageous because it allows the optical fiber 42 to passcompletely through the furcation unit 10 without coming in contact witheither the sealant material 15 or the material used in the adhesivematrix 43.

The unique features of this invention include a furcation unit whichprotects the fibers within a multi-fiber optical cable from damage,seals to the end of the multi-fiber optical cable, captures the strengthmembers within the individual loose tube single fiber cables within thefurcation unit and provides a single fiber connector and splicecompatible single fiber cable structure. The advantages of thisinvention include the low cost of the components used to construct thefurcation unit, the ruggedness of the furcation unit and the tensilestrength of the furcation unit.

Although the invention has been described relative to a specificembodiment thereof, there are numerous variations and modifications thatwill be readily apparent to those skilled in the art in the light of theabove teachings. It is therefore to be understood that, within the scopeof the appended claims, the invention may be practiced other than asspecifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. An assembly, including:a structure thatcontains a plurality of optical fibers; a furcation tube assembly thatincludes a plurality of loose tube optical fiber cables, wherein theplurality of optical fibers are coupled to respective ones of theplurality of loose tube optical fiber cables; and, a heat shrink tubethat joins the structure and the furcation tube assembly.
 2. Theassembly as set forth in claim 1, further including a protective tubesurrounded by the heat shrink tube and disposed in surroundingrelationship to the furcation tube assembly.
 3. The assembly as setforth in claim 2, wherein the protective tube is made of a rigidmaterial that provides structural support to withstand bending andtensile loads.
 4. The assembly as set forth in claim 3, wherein the heatshrink tube comprises an adhesive-coated heat shrink tube.
 5. Theassembly as set forth in claim 4, wherein the heat shrink tube comprisesa polyolefin tube.
 6. The assembly as set forth in claim 3, wherein therigid material comprises a plastic material.
 7. The assembly as setforth in claim 2, wherein the protective tube comprises a polyetheyleneplastic tube.
 8. The assembly as set forth in claim 2, wherein thehollow inner tube of each of the plurality of loose tube optical fibercables comprises a nylon tube.
 9. The assembly as set forth in claim 2,wherein the strength members of each of the plurality of loose tubeoptical fiber cables are comprised of an arimid fiber material.
 10. Theassembly as set forth in claim 9, wherein the adhesive matrix of each ofthe plurality of loose tube optical fiber cables comprises a two-partepoxy adhesive matrix.
 11. The assembly as set forth in claim 2, furtherincluding a spacer/fiber guide located within the protective tube todirect respective ones of the plurality of optical fibers from thestructure that contains the plurality of optical fibers to therespective ones of the plurality of loose tube optical fiber cables. 12.The assembly as set forth in claim 1, wherein each of the plurality ofloose tube optical fiber cables includes:a hollow inner tube; a supportstructure that includes strength members embedded in an adhesive matrix,the support structure surrounding the hollow inner tube; and, aprotective jacket surrounding the support structure.
 13. The assembly asset forth in claim 12, further including a protective tube surrounded bythe heat shrink tube and disposed in surrounding relationship to thefurcation tube assembly, wherein the protective tube is made of a rigidmaterial that provides structural support to withstand bending andtensile loads.
 14. The assembly as set forth in claim 13, wherein theheat shrink tube comprises an adhesive-coated heat shrink tube.
 15. Theassembly as set forth in claim 1, herein the structure comprises a fiberoptic cable.
 16. The assembly as set forth in claim 1, wherein theplurality of optical fibers include at least end portions that areunprotected.
 17. The assembly as set forth in claim 1, wherein theplurality of loose tube optical fiber cables are each coupled to a fiberoptic connector.
 18. The assembly as set forth in claim 1, wherein theplurality of loose tube optical fiber cables are each coupled to a fiberoptic splice.
 19. The assembly as set forth in claim 1, furtherincluding a sealant material that seals the structure that contains theplurality of optical fibers.
 20. The assembly as set forth in claim 1,wherein the heat shrink tube comprises an adhesive-coated heat shrinktube.
 21. A method, including the steps of:providing a structure thatcontains a plurality of optical fibers; providing a furcation tubeassembly that includes a plurality of loose tube optical fiber cables;joining the structure and the furcation tube assembly with a heat shrinktube; and, coupling the plurality of optical fibers to respective onesof the plurality of loose tube optical fiber cables.
 22. The method asset forth in claim 21, further including the step of assembling aprotective tube in surrounding relationship to the furcation tubeassembly and inside of the heat shrink tube in substantially concentricrelationship thereto.
 23. The method as set forth in claim 22, whereinthe protective tube is made of a rigid material that provides structuralsupport to withstand bending and tensile loads.
 24. The method as setforth in claim 23, wherein the heat shrink tube comprises anadhesive-coated heat shrink tube.
 25. The method as set forth in claim21, wherein the plurality of optical fibers include at least endportions that are unprotected.
 26. The method as set forth in claim 21,further including the step of connectorizing the plurality of loose tubeoptical fiber cables to a fiber optic connector.
 27. The method as setforth in claim 21, further including the step of connectorizing theplurality of loose tube optical fiber cables to a fiber optic splice.28. The method as set forth in claim 21, wherein the structure comprisesa fiber optic cable.
 29. The method as set forth in claim 21, whereinthe heat shrink tube comprises an adhesive-coated heat shrink tube. 30.The method as set forth in claim 21, wherein the step of providing afurcation tube assembly that includes a plurality of loose tube opticalfiber cables includes the sub-steps of:providing a plurality of hollowinner tubes; constructing a support structure by embedding a pluralityof strength members in an adhesive matrix in surrounding relationship tothe plurality of hollow inner tubes; and, assembling a protective jacketin surrounding relationship to the support structure.